The carbon is photoelectron spectrum of CO��� has been measured with very high photon energy resolution. The natural lifetime of the carbon is hole state has been determined from a series of spectra taken at photon energies of 308, 320, and 330 eV. The measured values of the lifetimes show a dependence on photon energy; this is attributed to failure of the theory of post-collision interaction to predict correctly the observed electron spectrum near threshold. The lifetime widths reported here are critically compared with those values from the literature that are based on other spectroscopic techniques. The oxygen 1s photoelectron spectrum for CO��� has been calculated using ab initio electronic structure theory, a localized hole simulated by the equivalent-cores approximation, and the harmonic oscillator approximation. There is good agreement between the calculated spectrum and a recently reported experimental spectrum. / Graduation date: 1999

No description available.

Thesis (B.S.)--Rochester Institute of Technology, 1983. / Typescript. Includes bibliographical references (leaf 17).

The study of semiconductor materials and more recently, artificially struc¬tured materials, is important for both scientific and industrial purposes. Many techniques have been developed to characterize the electronic properties of these materials. Optical characterization is a popular approach to this field of study, as the absorption or reflection of incident photons is directly related to the band structure of a semiconductor material. When measuring the absolute reflectivity or absorptivity, the resulting spec¬trum is often rather featureless, making it difficult to observe band structure features. This led to the invention of modulation spectroscopy techniques where the derivative of the absorptivity or reflectivity of a semiconductor ma¬terial with respect to some experimental parameter, is evaluated. Weak fea¬tures in the absolute spectrum are thus enhanced, making the identification of band structure features easier. This study describes the technique of photo reflection spectroscopy (com¬monly known as photoreflectance spectroscopy) where modulation is achiev¬ed optically. The theory behind photoreflectance spectroscopy is discussed in detail, whereafter the practical implementation is described. This is followed by measurements done on GaAs to do a basic comparison with published re¬sults. Finally, three different doping superlattices were investigated with this technique; including the influence that a-particle irradiation and consequent annealing have on the measured photoreflectance spectra. / Dissertation (MSc (Physics))--University of Pretoria, 2006. / Physics / unrestricted

The surface-specific analytical technique of X-ray photoelectron spectroscopy (XPS) is described, and was used to study various geochemical materials and organic compounds. Variation of surface pyrite density with coal particle size (53-250/µm) in a typical Canadian coal (Minto) provided some interesting data- it is very likely that as coal is crushed, one eventually reaches a particle size where the surface pyrite/carbon ratio maximizes. It is this parameter that is examined here, and correlations were found between (i) surface pyrite concentration,(ii) surface pyrite/sulfate ratio, and (iii) oxidized and non-oxidized sulfur with particle size. This is information which should find useful application in coal cleaning technology. For non-oxidized coal, we find the area of exposed pyrite on the coal surface is approximately inversely proportional to coal particle radius. However, for oxidized coal the appearance of curves depends on the oxidation times, but there is a particle size which exhibits maximum surface pyrite relative to 1/radius, corresponding to the intercept point of the two linear segments (low and higher values of 1/R) for the non-oxidized coal (fig. 3.9), and which is evidently that we will call the "characteristic" size of constituent pyrite. XPS 2p₃/₂ sulfur peaks from major sulfur constituents other than sulfate in sediment recovered from Mahoney Lake (south-central British Columbia, Canada) show a surprisingly periodic variation in sulfur 2p₃/₂ binding energy (BE), and hence molecular structure, with sediment age. The pattern ceases at a core depth of about 3.2 meters, where a major deposit of fine sandy sediment occurs just below ash deposition (2.6m) from a major eruption of Mount Mazama, Oregon, approximately 6500 year ago, which led to the formation of Crater Lake. Sedimental sulfur exists mainly as sulfate; however, there is a pronounced increase in amount of the lower BE sulfur species relative to sulfate toward lower depths. The "reduced" species also shows a trend towards slightly higher oxidation level at lower depths. We are able to suggest the probable chemical forms in which the sulfur species exist, which is of interest to biologists working on sulfur transformation studies in lakes. BE' s for nitrogen Is and sulfur 2p₃/₂ in the metal chelates of dibenzyldithiocarbamic acid M(DBDTC)n for n=2, M=Cu(II) and Zn(II), and for n=3, M=Bi(III), have been measured. The nature of the spectral peaks and core BE's indicates that the nitrogen atom in the DBDTC is not intramolecularly bound with the metal as had been previously suggested. The relatively high BE's for the nitrogen Is orbitals indicate planar geometry for the coordinated ligands, and the form [formula omitted] to reasonably represent their structure, which agrees with previous infrared studies. / Science, Faculty of / Chemistry, Department of / Graduate

Chiral molecules are composed of the same constituent atoms, but are inherently different due to being mirror images of each other. The physical properties of such molecules are nearly identical, but the biochemical interactions can differ wildly, which has extreme implications in the pharmaceutical industry. It is for this reason that it is important to be able to characterize and study individual enantiomers, and develop physical methods to do so. Optical techniques have evolved over the past two decades of scientific work which have been shown to be able to distinguish one enantiomer from another. These techniques tend to involve the use of circularly polarized light to induce a forward/backward asymmetry along the axis of light's propagation. The resulting sensitivity difference between enantiomers is typically on the order of a few percent. Recently, a novel optical pulse scheme has been developed whose electric field is fully three-dimensional and inherently chiral. This field was computationally used to demonstrate that the signal difference between enantiomers can reach upwards of 100\% sensitivity through the generation of high harmonics. Presented in this thesis are the results of an experimental measurement performed using just such a novel pulse scheme. A cold target recoil ion momentum spectroscopy machine is used to detect the photoelectron spectra from the ionization of each enantiomer of propylene oxide. A comprehensive discussion on the practical realization of the novel pulse scheme is presented, and the circular dichroism due to the novel field is shown. Also discussed are fragmentation of propylene oxide, three dimensional chiral signals found in the data, and a new measure to define the magnitude of chirality in a photoelectron distribution. Finally, measurements pertaining to the ionic yield of each enantiomer under varying handedness of light are shown. These results are the first experimental realization of optical measurements using synthetically designed chirality.

This dissertation describes a study of the electronic structure of some selected cyclopentadienyl metal olefin, (mu)-alkylidene, and carbonyl complexes. While most studies of this type are largely theoretical in nature, this work relies on the experimental observations which result from the application of photoelectron spectroscopy to the measurements of the important molecular energies of these compounds. The first part of the discussion is a study of metal-olefin bonding in the CpM(CO)₂L (L = C₂H₄, C₃H₆) compounds. Of particular interest are the observed changes in ionization energies of the olefin (pi) orbital upon coordination. These results also allow a comparison of the coordination of CO and C₂H₄. The valence ionizations of μ-CH₂-[(C₅H₄CH₃)Mn(CO)₂]₂ are also presented. This example of the increasingly important μ-alkylidene complexes provides evidence of a 3C-6e configuration with a net Mn-Mn single bond. The final chapter describes a study of the valence electronic structure of the CpM(CO)₂ (M = Co, Rh; Cp = η⁵-C₅H₅⁻) and η⁵-C₅(CH₃)₅⁻ ) system. This group of four closely related molecules demonstrates how photoelectron spectroscopy can be used to monitor the electronic effects of specific chemical modifications. The intent throughout is to not only present a detailed analysis of the specific compounds chosen for this study, but to also further demonstrate the applicability of photoelectron spectroscopy to a broad spectrum of problems concerning the structural and electronic make-up of organometallic molecules.

The details of the electronic structure and bonding in ferrocenes and early transition metal bent metallocenes are probed by photoelectron spectroscopy. The fundamental electronic interaction of the methyl group substituted for a hydrogen on a metal-coordinated cyclopentadienyl ring is shown by a combined core and valence pe spectroscopic study of a series of methyl-substituted ferrocenes. Shifts of core and valence ionization energies upon methyl substitution are equivalent and additive for the iron atom. Knowledge of the core ionization energy shifts for both carbon and iron allow the relative changes in atomic charges upon methyl substitution to be found. In these molecules, the methyl group is found not to be an inductive electron donor as is commonly assumed. The primary electronic effect of methyl substitution is on the valence orbitals of the cyclopentadienyl ring. Methylation of the cyclopentadienyl rings of ferrocene causes a dramatic redistribution of valence electron density and greatly increases the covalent nature of metal-ring bonding. An understanding of the electronic effect of methylation of metal-coordinated cyclopentadienyl rings is used to establish the relative locations of ring π and Cl ionizations in the pe spectra of group IV and V early transition metal bent metallocene dichlorides with both unsubstituted cyclopentadienyl and pentamethylcyclopentadienyl ligands. The differences in chloride and methyl ligand bonding to an early transition metal center are reflected in the photoelectron data of the dichlorides and related dimethyls. The relative differences in metal-chlorine and metal-carbon bond strengths are also shown in the pe data. The relationship between bond strengths and ionization energies is detailed for early transition metal bent metallocenes of niobium and tantalum with a variety of ligands. The relative bond strength/ionization energy information for metal-hydrogen and metal-carbon bonds is shown to help in understanding the stability of niobocene and tantalocene ethylene-hydride complexes and their resistance to intramolecular olefin insertion. Evidence from the pe data concerning the electron distribution as well as the relative bond strengths in these ethylene-hydride complexes is found supporting the consideration of these complexes more properly as metallacyclopropane-hydrides.

The corrosion chemistry of two active-metal systems has been studied primarily with X-ray Photoelectron Spectroscopy. First, the interaction of metallic lithium thin films with simple glass surfaces was investigated. Li was deposited on SiO₂, sodium silicate, potassium silicate, and B₂O₃ glasses in an ultra-high vacuum deposition and analysis chamber. The reaction of Li with SiO₂ results in substantial reduction of the glass matrix to form a thin product layer. A negatively-charged Si species was identified based on an unusually low XPS Si(2p) binding energy. The interaction of Li with alkali silicate glasses resulted in substantially less matrix breakdown than for SiO₂, but exchange of lithium for either sodium or potassium cations occurred at the Li/glass interface. The reaction between Li and B₂O₃ was limited to the top layers of the glass, as a passivating layer formed at the Li/B₂O₃ interface. Investigations into the oxidation of polycrystalline iron surfaces were initiated. Clean surfaces were exposed to controlled amounts of pure oxygen gas. The resulting oxide composition and thickness was determined using ultraviolet photoelectron spectroscopy (UPS), electron energy loss spectroscopy (EELS), and XPS. The results indicated the formation of a bilayer structure, with FeO near the oxide-metal interface, and Fe₃O₄ at the outer surface. Film growth was approximately logarithmic with time, and was strongly pressure dependent. Studies of the electronic properties of the characterized iron oxide surfaces were conducted by measuring the rate of electron transfer between the surface and redox-active species in an electrochemical cell. A strong dependence on film thickness was indicated. Photoemission of electrons from a solid is an inherently complex process; this is especially the case for XPS of clean and oxide-covered active metals. Improved theoretical models of XPS lineshapes were developed which provided new insight into the physical processes involved in photoemission. Additionally, these models provided improved qualitative and quantitative data interpretation through the use of least-squares fitting techniques.

The techniques of valence photoelectron spectroscopy (PES), X-ray diffraction, molecular orbital calculations, and multi-nuclear NMR are combined in a comparison of metal-phosphine bonding in a series of phosphine substituted molybdenum and tungsten metal carbonyl complexes, M(CO)(6-n)(P)(n) [n = 1,2,3,4,6]. The phosphine, P, represents either the mono-dentate phosphine, PMe₃, or one phosphine unit in the diphosphines, Me₂P(CH₂)ₓPMe₂, [x = 1, bis(dimethylphosphino)methane (DMPM); x = 2, 1,2-bis(dimethylphosphino)ethane (DMPE)]. Comparison of PMe₃ and the diphosphines in mono-dentate coordination (i.e. η¹-Mo(CO)₅DMPE) indicates the σ-donor strength is essentially identical for the three phosphines studied. Comparison of PMe₃ and the diphosphines in cis-chelating geometries reveals essentially identical charge at the coordinated phosphorus atoms and nearly identical charge at the metal center for cis-M(CO)₄(PMe₃)₂ and cis-M(CO)₄DMPE despite different local P-M-P bond angles. The X-ray crystal structures reveal a "twist" of the phosphine ligand when in sterically strained coordination geometries. The phosphine twist results in a "bent" metal-phosphine bond and is evaluated based on both electronic and steric considerations. The phosphine twist principle is used in studies on the nature of phosphine ligand electronic effects in the M(CO)(6-n)(P)(n) series at high substitution numbers, n. The PES data of the DMPE complexes for n = 4, cis-Mo(CO)₂(DMPE)₂, and n = 6, Mo(DMPE)₃, show symmetric metal electronic structure, but also a deviation from the previously observed additive behavior of phosphine electronic effects. The PES data for cis-Mo(CO)₂(PMe₃)₄ reveal a symmetric metal electronic structure due to sterically induced ligand-ligand interactions in this metal carbonyl complex. Multi-nuclear NMR data (³¹P and ⁹⁵Mo) are presented and the results discussed in light of the important ligand-ligand interactions observed in the PES studies. In addition, comparison of the NMR results for the mono-dentate and chelating phosphine complexes and the PES metal electronic structures provides a possible contribution to the ring chelate effect that is observed in the ³¹P and ⁹⁵Mo chemical shifts. The ring chelate effect refers to the unexplained relative differences between the ³¹P and ⁹⁵Mo chemical shifts of the cis-(PR₃)₂ complexes and the chelating diphosphine analogues.